The present invention relates to fastening mechanisms. In particular, the current invention is well suited for fastening printed wiring boards (PWBs) to mounting posts that are then attached to a frame of an electronic enclosure, or to another PWB.
Modern electronic systems, in particular, computer systems, comprise one or more processors, controllers, memory, and input/output devices such as floppy disk drives, hard disk drives, compact disk drives, for examples. Electronic circuitry, logic elements, and memory circuitry implementing the parts of an electronic system are constructed on silicon, or other suitable semiconductor, chips. The chips are typically mounted on modules that couple signals and power supply connections from the chip to connection points, or ports, on the modules. Historically, wire bonds have frequently been used to couple signals and power from a chip to electrical conductors on the module, the electrical conductors thereby continuing the electrical continuity to the ports on the module. A more recent means to couple signals and power from a chip to electrical conductors on the module is accomplished with solder ball connections. The chip with solder balls attached is placed upon a module, with the solder balls being in contact with electrical conductors on the module. The combined unit is heated to a temperature at which the solder ball connections melt, completing the electrical chip/module interconnection. Upon cooling the combined unit, the solder re-hardens, making a good mechanical connection, as well as the electrical interconnection. The modules are mounted on, and further interconnected by, printed wiring boards (PWBs). There are a number of techniques that are used to couple signal and power between a module and a PWB. One such technique is to place connecting pins on the module, the connecting pins being coupled to the signal and power conductors on the module. Often, the pins are brazed or soldered on the bottom of the module. The module is placed on the PWB with the pins inserted into holes in the PWB. The holes are plated with electrically conducting material that is coupled to conductors on one or more layers of patterned, electrically conducting, material in the PWB. The PWBs have signal wiring on one or more electrically conducting layers that couple signals between the various module ports, as well as to connectors from which signals and power conductors are routed to other places in the computer system.
The electronic system also comprises an enclosure inside which the PWBs, power supplies, and other components are housed. The enclosure can be made of any suitable material, such as plastic or metal. Metal is commonly used for the enclosure in order that a system (chassis) voltage (commonly ground) can be coupled to a voltage used on the PWBs (commonly ground) to supply power to circuitry on the semiconductor chips. For most systems, coupling ground used by circuitry on the semiconductor chips to chassis ground provides a short return path for common mode current.
The PWBs must be held in their proper place in the enclosure. A traditional method of mounting PWBs in computer system enclosures and support structures has been the use of threaded fasteners, such as screws and bolts. While this method does provide secure holding of the PWB in position, and also provides positive electrical contact, it does present several problems as discussed below.
First, the assembly of these threaded fasteners can be time consuming and often requires the use of tools. Torque must be carefully controlled to prevent damaging the PWB.
Second, the use of such threaded fasteners affects the packaging design and can cause compromising the design by requiring sufficient clearances for the tools and drivers needed to secure the threaded fasteners.
Third, during field repairs, the fastener may be difficult to access. The fasteners may be dropped into the interior of the enclosure and cause damage if not retrieved. Proper torque settings may be difficult to control during field repairs, raising the likelihood of the field repairs causing further damage to the product.
Some electronic products require a first PWB to be mounted to a second PWB. The disclosed fastener is capable of fastening the first PWB to the second PWB. The second PWB can then further be mounted to the enclosure by additional uses of the disclosed fasteners.
Therefore, there is a need for a fastener that can quickly and reliably connect a PWB mechanically and electrically to an enclosure, or to another PWB, without the use of tools.
The present invention discloses a fastener that can fasten and hold a substantially flat, planar, object to the fastener within a predetermined range of force, providing reliable electrical connection between the object and fastener, without the use of tools.
In an embodiment, the fastener connects a printed wiring board (PWB) to an enclosure.
In an embodiment, the fastener connects a first PWB to a second PWB.
In an embodiment, a clamp lever comprises a built-in spring that maintains a predetermined range of force between the PWB and the mounting post.
In an embodiment, the clamp lever is connected with a pin to the mounting post, allowing the clamp lever to be pivoted from a first position, substantially longitudinal with the axis of the mounting post, to a second position, substantially orthogonal to the axis of the mounting post. The action of pivoting the clamp lever deforms the built-in spring, compressing the PWB against a shoulder on the mounting post. The deformation of the built-in spring places a predetermined range of force between the PWB and the shoulder of the mounting post even considering normal process variations in the thickness of the PWB.
In an embodiment, the mounting post is constructed of a conducting material, such as metal. The action of pivoting the clamp lever and compressing the built-in spring creates an electrical connection between an electrically conductive area on the PWB and the mounting post. Advantageously, the mounting post is further electrically coupled to a chassis of the computer enclosure, thus allowing reliable coupling between a supply voltage used in semiconductor chips in the computer system and the computer enclosure.